DOC: Add a CITATION.cff file

[reshamas]

Issue with current documentation:

There is currently a CITATION.bib file in this repo. But, if a proper CITATION.cff file is set up:
a) it could be more visible to users
b) it could provide the citation in both the APA and BibTeX versions

Example:

• video: https://www.linkedin.com/feed/update/urn:li:activity:7232762440747302912/
• sample file: https://github.com/scikit-learn/scikit-learn/blob/main/CITATION.cff
• https://citation-file-format.github.io/#/tools-for-working-with-citationcff-files
• https://github.com/citation-file-format/cffconvert

What is a CITATION.cff file?

CITATION.cff files are plain text files with human- and machine-readable citation information for software (and datasets). Code developers can include them in their repositories to let others know how to correctly cite their software.

Idea or request for content:

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